Actually, the root of Tang Soo Do is from traditional Okinawa Karate - Tang Soo Do is the korean reading of "The Way of Chinese Hands". The root of TKD is from Shotokan Karate. The founder of TKD, General Choi, was awarded 2nd dan by Gichin Funakoshi, founder of Shotokan.
Just wanted to interject that there are lines of TKD that do not trace decent from General Choi. Choi is generally credited with coining the name TKD, but the technical background appears to have been much more of a comittee thing (unification of the Kwans) though most seem to have a Japanese influence to some degree. The Moo Duk Kwan lineage that I studied moves in a fashion totally different fashion (more similar to Karate) than what I saw of the Choi sine wave style.
There's some new books on the history of TKD that that I haven't gotten around to reading yet.